Chapter 9 InputOutput The Architecture of Computer Hardware

Chapter 9: Input/Output The Architecture of Computer Hardware and Systems Software: An Information Technology Approach 3 rd Edition, Irv Englander John Wiley and Sons 2003

Basic Model § Processing speed or program execution § determined primarily by ability of I/O operations to stay ahead of processor. Input Chapter 9 Input / Output Process Output 2

I/O Considerations Speed Issues § CPU operates at speeds much faster than the fastest I/O device § Devices operate at different speeds § Bursts of data § Block data transfer required for some devices Coordination § § Several devices perform I/O simultaneously Unexpected input Various input formats Status information needed for each device Chapter 9 Input / Output 3

I/O Device Interface Issues § Different formats § parallel interface § serial interface § Buffering of data § Burst vs. stream § Different control requirements § electromechanical Chapter 9 Input / Output 4

Examples of I/O Devices Chapter 9 Input / Output 5

Simple I/O Configuration Chapter 9 Input / Output 6

I/O Modules Functions § Recognizes messages from device(s) addressed to it and accepts commands from the CPU § Provides a buffer where the data from memory can be held until it can be transferred to the disk § Provides the necessary registers and controls to perform a direct memory transfer § Physically controls the device § Copies data from its buffer to the device/from the CPU to its buffer § Notifies with interrupts Chapter 9 Input / Output 7

Input/Output Modules § Programmed I/O § CPU controlled I/O § Interrupt Driven I/O § External input controls § Direct Memory Access Controllers § Method for transferring data between main memory and a device that bypasses the CPU Chapter 9 Input / Output 8

Programmed I/O § I/O data and address registers in CPU § One word transfers § Address information for each I/O device § LMC I/O capability for 100 devices § Full instruction fetch/execute cycle § Primary use: § keyboards § communication with I/O modules (see DMA) Chapter 9 Input / Output 9

Programmed I/O Chapter 9 Input / Output 10

Programmed I/O Example Chapter 9 Input / Output 11

Programmed I/O Example Chapter 9 Input / Output 12

Interrupts § Signal that causes the CPU to alter its normal flow on instruction execution § frees CPU from waiting for events § provides control for external input § Examples § § unexpected input abnormal situation illegal instructions multitasking, multiprocessing Chapter 9 Input / Output 13

The CPU - The Interrupt Cycle § Fetch / Execute cycle § Interrupt cycle START Fetch Next Instruction HALT Execute Instruction Interrupts Disabled Check/Process Interrupt Chapter 9 Input / Output 14

Interrupt Terminology § Interrupt lines (hardware) § Interrupt request § Interrupt handlers § Program that services the interrupt § Also known as an interrupt routine § Process Control Block (PCB) § Located in a part of memory known as the stack area § All registers of a program are saved here before control is transferred to the interrupt handler Chapter 9 Input / Output 15

Interrupt Terminology § Servicing the interrupt § suspends program in progress § saves pertinent information including last instruction executed and data values in registers in the PCB (process control block) § branches to interrupt handler Chapter 9 Input / Output 16

Servicing an Interrupt Chapter 9 Input / Output 17

Use of Interrupts § Notify that an external event has occurred § real-time or time-sensitive § Signal completion § printer ready or buffer full § Allocate CPU time § time sharing § Indicate abnormal event (CPU originates for notification and recovery) § illegal operation, hardware error § Software interrupts Chapter 9 Input / Output 18

Multiple Interrupts § Identifying devices § Polling (checking for input in rotation) § Vectored interrupts (include address of interrupting device) § Interrupt priorities § Loss of data vs. task completion § Maskable (disabled) interrupts Chapter 9 Input / Output 19

Vectored Interrupts Chapter 9 Input / Output 20

Polled Interrupts Chapter 9 Input / Output 21

Multiple Interrupts Example Chapter 9 Input / Output 22

Direct Memory Access § § Transferring large blocks of data Direct transfer to and from memory CPU not actively involved in transfer itself Required conditions for DMA § The I/O interface and memory must be connected § The I/O module must be capable of reading and writing to memory § Conflicts between the CPU and the I/O module must be avoided Chapter 9 Input / Output 23

DMA Instruction Set § Application program requests I/O service from operating system § § privileged instructions To initiate DMA, programmed I/O is used to send the following information: 1. 2. 3. 4. § location of data on I/O device the starting location in memory the size of the block read/write Interrupt to CPU upon completion Chapter 9 Input / Output 24

DMA Initiation and Control Chapter 9 Input / Output 25

Basic CPU-Memory-I/O Pathway* Chapter 9 Input / Output 26

Bus Configuration Chapter 9 Input / Output 27

Bus Characteristics § Data width in bits carried simultaneously § Throughput, i. e. , data transfer rate in bits per second § Point-to-Point vs. Multipoint § Parallel vs. Serial § Use § Distance § Protocol Chapter 9 Input / Output 28

Bus Hierarchy § Processor bus: on-chip § Cache bus (backside bus) § Memory bus (front-side bus) § connects the memory subsystem and processor § Local I/O bus § high-speed bus used to connect performance critical peripherals to memory and processor § Examples: PCI, VESA Local Bus § Standard I/O bus § connects slower peripherals (ISA) to Local I/O bus Chapter 9 Input / Output 29

Wintel Bus Systems § § ISA: Industry Standard Architecture MCA: Micro Channel Architecture EISA: Extended Industry Standard Architecture Local Bus § PCI: Peripheral Component Interconnect (also Apple, Sun, Compaq Alpha Server) § VLB: VESA (Video Electronics Standards Association) Local Bus § AGP: Accelerated Graphics Port § Point-to-point channel from graphics controller to main memory § Co-exists with PCI Chapter 9 Input / Output 30

Compaq 7000 and 10000 System Architecture Chapter 9 Input / Output 31

External Interface Buses and Ports § Parallel port § Serial port § RS-232 C and RS-422 buses § SCSI § Small Computer System Interface § USB, USB-2 § Universal Serial Bus § IEEE 1394 § Firewire § i. link Chapter 9 Input / Output 32

SCSI Bus § ANSI standard but multiple variations § Really an I/O bus rather than simple interface § Supports multiple devices from a single SCSI port Chapter 9 Input / Output 33

USB § Multipoint bus § Hubs provide multiple connection points for I/O devices § Supports 127 devices Topology Example Root Hub Hub Chapter 9 Input / Output 34

USB and Fire. Wire (IEEE 1394) § Both serial, multipoint bus specifications § Add/remove devices w/o powering down § Packet protocol for isochronous data transfer § Isochronous: delivery at regular time intervals § Guarantee specified throughput Chapter 9 Input / Output 35

USB vs. Fire. Wire § USB: slow to medium speed data transfer applications, i. e. , storage devices § 12 Mbits/sec § USB-2: high-speed data transfer § 480 Mbits/sec § Fire. Wire: high-speed data transfer, i. e. , full motion video with sound § 400 Mbits/sec to 3. 2 Gbits/sec Chapter 9 Input / Output 36

Typical Fire. Wire Configuration § Network-like characteristics § Device controllers independent Chapter 9 Input / Output 37

Channel Architecture § Used in IBM mainframe computers § Channel subsystem § Separate I/O processor that serves as a CPU for I/O operations § Channel control words § Programs that transfer data between memory and an I/O device using DMA § Subchannels § Connected to a control unit module through one or more channel paths § Similar role to a device controller Chapter 9 Input / Output 38

I/O Channel Architecture Chapter 9 Input / Output 39